Ammonium nitrate

Ammonium nitrate is a white crystalline chemical compound most commonly used in fertilizers and explosives. An artificially produced substance, it ranks among the most widely manufactured chemicals in the United States. Due to its potential volatility, ammonium nitrate can be very dangerous and has, on several occasions, caused devastating explosions. Despite these risks, however, it remains in demand thanks to its many practical uses.

Overview

Ammonium nitrate is a solid compound made out of nitrogen, hydrogen, and oxygen molecules. It is formulaically denoted as NH4NO3 and has a molecular weight of 80.04 g/mol. It melts at 169.6°C (337.3°F) and boils at 211°C (412°F). When it passes its boiling point, it decomposes explosively. In addition to being highly soluble in water, it is also soluble in alcohol and acetone. Due to this solubility, it is unable to occur naturally in the environment.

Ammonium nitrate was first produced by German chemist Johann Rudolf Glauber in 1659. Glauber found that if he passed ammonia gas and a water-based solution of nitric acid through a pipe, the ammonia would combine with the nitric acid and ultimately yield ammonium nitrate. Originally, he called the substance nitrum flammans, which means flaming nitre in Latin.

Uses

Although it has many potential applications, ammonium nitrate is primarily used as a component in fertilizers because of its nitrogen content. Plants rely on nitrogen to build the proteins to sustain themselves and grow. Most plants, however, lack sufficient energy to break down the strong molecular bond of atmospheric nitrogen. As a result, they have to acquire the nitrogen they need from other sources. Typically, plants gain access to nitrogen with the help of special nitrogen-fixing bacteria that combine atmospheric nitrogen with hydrogen to create ammonia. It is also possible to supply plants with nitrogen by treating them with fertilizers made from chemical compounds with weaker molecular bonds that allow the plants easier access to the nitrogen they need. Ammonium nitrate is used in a wide variety of fertilizers as a source of easily accessible nitrogen for plants. Millions of metric tons of ammonium nitrate-based fertilizer are produced in the United States every year.

Ammonium nitrate is also used to make various types of explosives. In this application, ammonium nitrate serves as a source of oxygen, which fuels the ignition of other materials and leads to an explosion. It is especially effective for this purpose because the explosive reaction it creates is particularly violent and long-lasting. Ammonium nitrate also is an ideal component for explosives because it is largely stable at normal temperatures and therefore relatively safe to store. Its stability results from the fact that it requires significant activation energy to ignite. Activation energy is the energy required for a chemical reaction to occur.

Ammonium nitrate has other applications beyond fertilizers and explosives. Thanks to its volatile properties, it is often used in the production of fireworks. It is also used in both rocket fuel and matches as a source of the oxygen necessary for ignition to occur. In addition, ammonium nitrate is frequently used in the production of nitrous oxide, a substance commonly known as laughing gas. Finally, it is also used as a nutrient for growing yeast and manufacturing antibiotics.

Notable Ammonium Nitrate Disasters

Although its relative stability makes it fairly safe under normal circumstances, ammonium nitrate can be very dangerous. On several notable occasions, ammonium nitrate was the key factor in disastrous explosions that caused extensive damage and loss of life. The most famous of these was an explosion that took place on board a cargo ship docked at Texas City, Texas, in 1947. As cargo was being loaded onto the ship, a fire broke out in its hold, which was filled with 17 million pounds of ammonium nitrate at the time. Before long, the fire ignited the ammonium nitrate and caused a massive explosion that could be felt up to 250 miles away. The accident killed 581 people and injured thousands more. Experts later called it the worst industrial accident in American history.

In 1995, American domestic terrorists Timothy McVeigh and Terry Nichols used ammonium nitrate and other chemicals to create a powerful car bomb that they detonated at the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma. The resulting explosion destroyed the building and caused numerous deaths and injuries.

Another accidental ammonium nitrate explosion occurred in West, Texas, in April 2013. A fire at the West Fertilizer Company ignited stores of ammonium nitrate and anhydrous ammonia and caused an explosion so powerful that it registered as a 2.1 magnitude earthquake at some geological monitoring stations. The explosion killed five people and injured nearly 200 others. It also caused damage to more than 50 nearby homes.

In light of these and other incidents, efforts have been made to ensure that ammonium nitrate is stored and handled properly and that it remains out of the hands of those who would use it for inappropriate purposes. Most notably, the Department of Homeland Security in 2011 put forth a proposition for an ammonium nitrate registration program that would oversee all transactions involving the transfer of ammonium nitrate at the point of sale.

Bibliography

Babrauskas, V. "Explosions of Ammonium Nitrate Fertilizer in Storage or Transportation Are Preventable Accidents." Journal of Hazardous Materials, vol. 304, 2016, pp. 134–49.

Di Justo, Patrick. "The Fertilizer Bomb." New Yorker. 18 Apr. 2013. Web. 21 Jan. 2015. http://www.newyorker.com/tech/elements/the-fertilizer-bomb

Fehling, Dave. "Dangerous Ammonium Nitrate Fertilizer Losing Favor in Texas." NPR StateImpact, 4 Nov. 2015, stateimpact.npr.org/texas/2015/11/04/dangerous-ammonium-nitrate-fertilizer-losing-favor-in-texas/.

Kershner, Kate. "Why Does Fertilizer Explode?" How Stuff Works. InfoSpace LCC. 19 Apr. 2013. Web. 21 Jan. 2015. http://science.howstuffworks.com/why-does-fertilizer-explode1.htm

Koerth-Baker, Maggie. "Ammonium Nitrate Fertilizer Isn't Really a Dangerous Explosive (Most of the Time)." BoingBoing. BoingBoing. 18 Apr. 2013. Web. 21 Jan. 2015. http://boingboing.net/2013/04/18/ammonium-nitrate-fertilizer-is.html

Schlager, Neil, Jayne Weisblatt, and David E. Newton, eds. "Ammonium Nitrate." Chemical Compounds. Vol. 1. Detroit: UXL, 2006. 73–76. Print.